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io_uring: ensure consistent view of original task ->mm from SQPOLL 

Ensure we get a valid view of the task mm, by using task_lock() when
attempting to grab the original task mm.

Reported-by: syzbot+b57abf7ee60829090495@syzkaller.appspotmail.com
Fixes: 2aede0e417 ("io_uring: stash ctx task reference for SQPOLL")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-11-02 10:39:05 -07:00
parent fdaf083cdf
commit 4b70cf9dea
1 changed files with 20 additions and 7 deletions
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25
fs/io_uring.c
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@ -995,20 +995,33 @@ static void io_sq_thread_drop_mm(void)
if (mm) {
kthread_unuse_mm(mm);
mmput(mm);
current->mm = NULL;
}
}
static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx)
{
if (!current->mm) {
if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) ||
!ctx->sqo_task->mm ||
!mmget_not_zero(ctx->sqo_task->mm)))
struct mm_struct *mm;
if (current->mm)
return 0;
/* Should never happen */
if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL)))
return -EFAULT;
kthread_use_mm(ctx->sqo_task->mm);
task_lock(ctx->sqo_task);
mm = ctx->sqo_task->mm;
if (unlikely(!mm || !mmget_not_zero(mm)))
mm = NULL;
task_unlock(ctx->sqo_task);
if (mm) {
kthread_use_mm(mm);
return 0;
}
return 0;
return -EFAULT;
}
static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,